In a motor vehicle comprising a heat engine and a rotary electric machine such as a starter alternator, such a machine comprises, in a non-limiting manner:                a rotor comprising an inductor in which an excitation current is conducted; and        a stator comprising a multi-phase winding.        
The starter alternator operates in motor mode or in generator mode.
This machine is referred to as being reversible.
In alternator mode, also referred to as generator mode, the machine makes it possible to transform a rotary movement of the rotor driven by the heat engine of the vehicle into an electric current induced in the phases of the stator. In this case a bridge rectifier connected to the phases of the stator makes it possible to rectify the induced sinusoidal current into a continuous current in order to supply consumers of the vehicle as well as a battery.
By contrast, in motor mode the electric machine acts as an electric motor making it possible to drive in rotation the heat engine of the vehicle via the rotor shaft. It makes it possible to transform the electrical energy into mechanical energy: In this case a converter makes it possible to transform a direct current originating from the battery into an alternating current in order to supply the phases of the stator in order to turn the rotor.
Control components are used in order to determine the operating mode of the rotary electric machine (motor mode or generator mode) via control signals.
The starter alternators that integrate a regenerative braking function and a function of heat engine acceleration assistance, referred to as mild hybrid starter alternators, also integrate filtering components that prevent the power components from interfering with the electrical network of the motor vehicle, generally a network of 48 volts. These reversible machines have powers of approximately 8 to 15 kW.
The power components (bridge rectifier and converter), the control components and also the filtering components generate heat. It is thus necessary to use a cooling device in order to dissipate this heat emitted by all these components.
Patent FR2847085 describes an electronic assembly comprising the power components and the control components (referred to as control units), the two sets of components being placed as close as possible to one another, and a cooling device for cooling this assembly. The cooling device comprises:                a dissipator on which the power and control components are mounted, the dissipator being arranged on the rear bearing of the electric machine and comprising fins on its lower face, which faces the bearing. In addition, there is a free space between the rotation shaft of the rotor and the dissipator, through which space air can circulate;        the rear bearing comprising radial air outlet holes; and        a protective cover comprising openings arranged on the top of said cover.        
Thus, some of the air is sucked laterally into the starter alternator and flows towards the radial outlet holes of the bearing, while sweeping over the fins of the dissipator, and the remaining air is sucked through the openings in the cover and then flows axially along the rotation shaft (via the free space) of the rotor so as to join a flow passage below the dissipator. Thus, the assembly of power and control components is cooled.
One disadvantage of this prior art lies in the fact that it does not offer any solution for thermal decoupling between the different blocks of electronic components in relation to their own dissipation needs. Now, in the context of the “mild-hybrid” application, a thermal decoupling must be effected notably between the power components and the filtering components. This is because the power components can reach operating temperatures which can be dangerous for the filtering components and consequently damage them.
In this context, the object of the present invention is to overcome the above-mentioned disadvantage.